xfs_quota

SYNOPSIS

DESCRIPTION

xfs_quota is a utility for reporting and editing various aspects of
filesystem quota.
The options to xfs_quota are:
-c cmd xfs_quota commands may be run interactively (the default) or
as arguments on the command line. Multiple -c arguments may
be given. The commands are run in the sequence given, then
the program exits.
-p prog Set the program name for prompts and some error messages, the
default value is xfs_quota.
-x Enable expert mode. All of the administrative commands (see
the ADMINISTRATOR COMMANDS section below) which allow modifi-
cations to the quota system are available only in expert
mode.
-d project
Project names or numeric identifiers may be specified with
this option, which restricts the output of the individual
xfs_quota commands to the set of projects specified. Multiple
-d arguments may be given.
-V Prints the version number and exits.
The optional path argument(s) can be used to specify mount points or
device files which identify XFS filesystems. The output of the individ-
ual xfs_quota commands will then be restricted to the set of filesys-
tems specified.
This manual page is divided into two sections - firstly, information
for users of filesystems with quota enabled, and the xfs_quota commands
of interest to such users; and then information which is useful only to
administrators of XFS filesystems using quota and the quota commands
which allow modifications to the quota system.
Note that common to almost all of the individual commands described
below are the options for specifying which quota types are of interest
- user quota (-u), group quota (-g), and/or project quota (-p). Also,
several commands provide options to operate on "blocks used" (-b),
"inodes used" (-i), and/or "realtime blocks used" (-r).
Many commands also have extensive online help. Use the help command for
more details on any command.
The quota command provides information on the quotas that have been set
by the system administrators and current usage.
There are four numbers for each limit: current usage, soft limit
(quota), hard limit, and time limit. The soft limit is the number of
1K-blocks (or files) that the user is expected to remain below. The
hard limit cannot be exceeded. If a user's usage reaches the hard
limit, further requests for space (or attempts to create a file) fail
with the "Quota exceeded" (EDQUOT) error.
When a user exceeds the soft limit, the timer is enabled. Any time the
quota drops below the soft limits, the timer is disabled. If the timer
pops, the particular limit that has been exceeded is treated as if the
hard limit has been reached, and no more resources are allocated to the
user. The only way to reset this condition, short of turning off limit
enforcement or increasing the limit, is to reduce usage below quota.
Only the superuser (i.e. a sufficiently capable process) can set the
time limits and this is done on a per filesystem basis.
Surviving When the Quota Limit Is Reached
In most cases, the only way for a user to recover from over-quota con-
ditions is to abort whatever activity is in progress on the filesystem
that has reached its limit, remove sufficient files to bring the limit
back below quota, and retry the failed program.
However, if a user is in the editor and a write fails because of an
over quota situation, that is not a suitable course of action. It is
most likely that initially attempting to write the file has truncated
its previous contents, so if the editor is aborted without correctly
writing the file, not only are the recent changes lost, but possibly
much, or even all, of the contents that previously existed.
There are several possible safe exits for a user caught in this situa-
tion. He can use the editor shell escape command to examine his file
space and remove surplus files. Alternatively, using sh(1), he can
suspend the editor, remove some files, then resume it. A third possi-
bility is to write the file to some other filesystem (perhaps to a file
on /tmp) where the user's quota has not been exceeded. Then after rec-
tifying the quota situation, the file can be moved back to the filesys-
tem it belongs on.

USER COMMANDS

print Lists all paths with devices/project identifiers. The path list
can come from several places - the command line, the mount ta-
ble, and the /etc/projects file.
df See the free command.
quota [ -g | -p | -u ] [ -bir ] [ -hnNv ] [ -f file ] [ ID | name ] ...
Show individual usage and limits, for a single user name or
numeric user ID. The -h option reports in a "human-readable"
format similar to the df(1) command. The -n option reports the
numeric IDs rather than the name. The -N option omits the
Online help for all commands, or one specific command.
quit Exit xfs_quota.
q See the quit command.

QUOTA ADMINISTRATION

The XFS quota system differs to that of other filesystems in a number
of ways. Most importantly, XFS considers quota information as filesys-
tem metadata and uses journaling to provide a higher level guarantee of
consistency. As such, it is administered differently, in particular:
1. The quotacheck command has no effect on XFS filesystems. The
first time quota accounting is turned on (at mount time), XFS
does an automatic quotacheck internally; afterwards, the quota
system will always be completely consistent until quotas are
manually turned off.
2. There is no need for quota file(s) in the root of the XFS
filesystem.
3. XFS distinguishes between quota accounting and limit enforce-
ment. Quota accounting must be turned on at the time of mount-
ing the XFS filesystem. However, it is possible to turn on/off
limit enforcement any time quota accounting is turned on. The
"quota" option to the mount command turns on both (user) quota
accounting and enforcement. The "uqnoenforce" option must be
used to turn on user accounting with limit enforcement disabled.
4. Turning on quotas on the root filesystem is slightly different
from the above. For IRIX XFS, refer to quotaon(1M). For Linux
XFS, the quota mount flags must be passed in with the "root-
flags=" boot parameter.
5. It is useful to use the state to monitor the XFS quota subsystem
at various stages - it can be used to see if quotas are turned
on, and also to monitor the space occupied by the quota system
itself..
6. There is a mechanism built into xfsdump that allows quota limit
information to be backed up for later restoration, should the
need arise.
7. Quota limits cannot be set before turning on quotas on.
8. XFS filesystems keep quota accounting on the superuser (user ID
zero), and the tool will display the superuser's usage informa-
tion. However, limits are never enforced on the superuser (nor
are they enforced for group and project ID zero).
9. XFS filesystems perform quota accounting whether the user has
quota limits or not.
/etc/projects file.
report [ -gpu ] [ -bir ] [ -ahntlLNU ] [ -f file ]
Report filesystem quota information. This reports all quota
usage for a filesystem, for the specified quota type (u/g/p
and/or blocks/inodes/realtime). It reports blocks in 1KB units
by default. The -h option reports in a "human-readable" format
similar to the df(1) command. The -f option outputs the report
to file instead of stdout. The -a option reports on all filesys-
tems. By default, outputs the name of the user/group/project. If
no name is defined for a given ID, outputs the numeric ID
instead. The -n option outputs the numeric ID instead of the
name. The -L and -U options specify lower and upper ID bounds to
report on. If upper/lower bounds are specified, then by default
only the IDs will be displayed in output; with the -l option, a
lookup will be performed to translate these IDs to names. The -N
option reports information without the header line. The -t
option performs a terse report.
state [ -gpu ] [ -av ] [ -f file ]
Report overall quota state information. This reports on the
state of quota accounting, quota enforcement, and the number of
extents being used by quota metadata within the filesystem. The
-f option outputs state information to file instead of stdout.
The -a option reports state on all filesystems and not just the
current path.
limit [ -g | -p | -u ] bsoft=N | bhard=N | isoft=N | ihard=N | rtb-
soft=N | rtbhard=N -d | id | name
Set quota block limits (bhard/bsoft), inode count limits
(ihard/isoft) and/or realtime block limits (rtbhard/rtbsoft).
The -d option (defaults) can be used to set the default value
that will be used, otherwise a specific user/group/project name
or numeric identifier must be specified.
timer [ -g | -p | -u ] [ -bir ] value
Allows the quota enforcement timeout (i.e. the amount of time
allowed to pass before the soft limits are enforced as the hard
limits) to be modified. The current timeout setting can be dis-
played using the state command. The value argument is a number
of seconds, but units of 'minutes', 'hours', 'days', and 'weeks'
are also understood (as are their abbreviations 'm', 'h', 'd',
and 'w').
warn [ -g | -p | -u ] [ -bir ] value -d | id | name
Allows the quota warnings limit (i.e. the number of times a
warning will be send to someone over quota) to be viewed and
modified. The -d option (defaults) can be used to set the
default time that will be used, otherwise a specific
user/group/project name or numeric identifier must be specified.
NOTE: this feature is not currently implemented.
the current path. Quota can only be switched back on subse-
quently by unmounting and then mounting again.
remove [ -gpu ] [ -v ]
Remove any space allocated to quota metadata from the filesystem
identified by the current path. Quota must not be enabled on
the filesystem, else this operation will report an error.
dump [ -g | -p | -u ] [ -f file ]
Dump out quota limit information for backup utilities, either to
standard output (default) or to a file. This is only the lim-
its, not the usage information, of course.
restore [ -g | -p | -u ] [ -f file ]
Restore quota limits from a backup file. The file must be in
the format produced by the dump command.
quot [ -g | -p | -u ] [ -bir ] [ -acnv ] [ -f file ]
Summarize filesystem ownership, by user, group or project. This
command uses a special XFS "bulkstat" interface to quickly scan
an entire filesystem and report usage information. This command
can be used even when filesystem quota are not enabled, as it is
a full-filesystem scan (it may also take a long time...). The -a
option displays information on all filesystems. The -c option
displays a histogram instead of a report. The -n option displays
numeric IDs rather than names. The -v option displays verbose
information. The -f option send the output to file instead of
stdout.
project [ -cCs [ -d depth ] [ -p path ] id | name ]
The -c, -C, and -s options allow the directory tree quota mecha-
nism to be maintained. -d allows to limit recursion level when
processing project directories and -p allows to specify project
paths at command line ( instead of /etc/projects ). All options
are discussed in detail below.

DIRECTORY TREE QUOTA

The project quota mechanism in XFS can be used to implement a form of
directory tree quota, where a specified directory and all of the files
and subdirectories below it (i.e. a tree) can be restricted to using a
subset of the available space in the filesystem.
A managed tree must be setup initially using the -s option to the
project command. The specified project name or identifier is matched to
one or more trees defined in /etc/projects, and these trees are then
recursively descended to mark the affected inodes as being part of that
tree. This process sets an inode flag and the project identifier on
every file in the affected tree. Once this has been done, new files
created in the tree will automatically be accounted to the tree based
on their project identifier. An attempt to create a hard link to a
file in the tree will only succeed if the project identifier matches
the project identifier for the tree. The xfs_io utility can be used to
specify project paths in command line without a need for /etc/projects
to exist. Note that if projects file exists then it is also used.

CAVEATS

XFS implements delayed allocation (aka. allocate-on-flush) and this has
implications for the quota subsystem. Since quota accounting can only
be done when blocks are actually allocated, it is possible to issue
(buffered) writes into a file and not see the usage immediately
updated. Only when the data is actually written out, either via one of
the kernels flushing mechanisms, or via a manual sync(2), will the
usage reported reflect what has actually been written.
In addition, the XFS allocation mechanism will always reserve the maxi-
mum amount of space required before proceeding with an allocation. If
insufficient space for this reservation is available, due to the block
quota limit being reached for example, this may result in the alloca-
tion failing even though there is sufficient space. Quota enforcement
can thus sometimes happen in situations where the user is under quota
and the end result of some operation would still have left the user
under quota had the operation been allowed to run its course. This
additional overhead is typically in the range of tens of blocks.
Both of these properties are unavoidable side effects of the way XFS
operates, so should be kept in mind when assigning block limits.